For transmission of electromagnetic signals, in particular of radio-frequency signals suitable receivers are required.
A conventional receiver design is for instance illustrated in FIG. 1. The signal receiver 1 comprises an antenna 12 for receiving electromagnetic signals. The antenna 12 is connected with a low noise amplifier (LNA) 14 that is adapted to amplify the signals received by the antenna 12. The LNA is further connected with a mixer 16 for mixing the amplified and received signals with an oscillating signal 50 provided by a local oscillator or by a crystal oscillator 20. The output of the mixer 16 is connected to a band-pass filter 18 to filter the intermediate and down-converted signals 40 of the mixer 16. In FIG. 1, the spectrum of the intermediate signals 40 is shown as amplitude or power (p) over frequency (f).
Typically, the local oscillator or crystal oscillator 20 makes use of a signal generator 24 with a reference resonator 22 such like a quartz resonator, providing a well-defined and rather stable reference frequency signal. For instance with typical quartz resonator applications, the signal generator 24 with the reference resonator 22 operates at a reference frequency of 26 MHz. Generally the local oscillator 20 further includes a PLL unit not shown in FIG. 1, which is connected between the signal generator 24 and the mixer 16, in order to supply a high frequency oscillating signal. In case of radio-frequency transmission the signal receiver 1 may for instance operate in a Bluetooth range, hence in the 2.4 GHz band by making use of a signal generator 24 with a quartz-based reference resonator 22 operating at 26 MHz. The 93rd, 94th and 95th higher harmonics of the frequency of the oscillator 20 based on the reference resonator 22 may then coincide with the band 41 of the band-pass filter 18.
Even though these higher harmonic components 42 of the oscillator based on the reference resonator could be damped and attenuated the electromagnetic signals received by the antenna, in particular the intermediate signals 40 received after the down-conversion by the mixer 16 may still be severely perturbed. This problem becomes even more dominant when the signal receiver is implemented in a single integrated circuit.
Another conventional receiver for FSK radio-frequency signals with a high sensitivity demodulator is for instance described in US Patent Application No. 2012/0164966 A1.
US Patent Application No. 2012/0046005 A1 describes a wireless communication device with a duty cycle control of an oscillator. This device needs operating simultaneously a tune transmit path and a receive path for regulating the duty cycle, which is a drawback.